Amelogenesis imperfecta (AI) (amelogenesis - enamel formation; imperfecta - imperfect) is a disorder that affects the structure and appearance of the enamel of the teeth. This condition causes teeth to be unusually small, discolored, pitted or grooved, and prone to rapid wear and breakage. These dental problems, which vary among affected individuals, can affect both primary (baby) teeth and permanent teeth. There are 4 main types of AI that are classified based on the type of enamel defect. These 4 types are divided further into 14 subtypes, which are distinguished by their specific dental abnormalities and by their pattern of inheritance.[1] AI can be inherited in an autosomal dominant, autosomal recessive or X-linked recessive pattern.[2]

Last updated: 12/12/2013

How is amelogenesis imperfecta inherited?

Amelogenesis imperfecta can have different patterns of inheritance, depending on the gene that is altered. Most cases are caused by mutations in the ENAM gene and are inherited in an autosomal dominant pattern. This type of inheritance means one copy of the altered gene in each cell is sufficient to cause the disorder.[2]

Amelogenesis imperfecta may also be inherited in an autosomal recessive pattern; this form of the disorder can result from mutations in the ENAM or MMP20 gene. Autosomal recessive inheritance means two copies of the gene in each cell are altered.[2]

About 5 percent of amelogenesis imperfecta cases are caused by mutations in the AMELX gene and are inherited in an X-linked pattern. A condition is considered X-linked if the mutated gene that causes the disorder is located on the X chromosome, one of the two sex chromosomes. In most cases, males with X-linked amelogenesis imperfecta experience more severe dental abnormalities than females with this form of this condition.[2]

Other cases of amelogenesis imperfecta result from new mutations in these genes and occur in people with no history of the disorder in their family.[2]

Last updated: 9/17/2015

What causes amelogenesis imperfecta?

Amelogenesis imperfecta is caused by mutations in the AMELX, ENAM, and MMP20 genes. These genes provide instructions for making proteins that are essential for normal tooth development. These proteins are involved in the formation of enamel, which is the hard, calcium-rich material that forms the protective outer layer of each tooth. Mutations in any of these genes alter the structure of these proteins or prevent the genes from making any protein at all. As a result, tooth enamel is abnormally thin or soft and may have a yellow or brown color. Teeth with defective enamel are weak and easily damaged.[2]

In some cases, the genetic cause of amelogenesis imperfecta can not been identified. Researchers are working to find mutations in other genes that are responsible for this disorder.[2]

Click on each gene name to learn more about the role it plays in the development of tooth enamel.

Last updated: 9/17/2015

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